Santa Cruz Islands Research Articles

Typological thinking and the conservation of subspecies: the case of the San Clemente Island loggerhead shrike

Abstract. Hybridization with closely related taxa poses a significant threat to endangered subspecies (e.g. outbreeding depression, inbreeding) and confounds efforts to manage and conserve these taxa through a loss of taxonomic identity, in part because of the practical necessity of defining subspecies in a typological manner. We examined nine morphological characters in 167 post‐juvenile museum specimens to determine if loggerhead shrikes Lanius ludovicianus Linnaeus 1766 on San Clemente Island (off the coast of California) remain diagnosable as L. l. mearnsi Ridgway (1903); an island endemic listed as endangered by the United States Fish and Wildlife Service. Four recent shrike specimens from the island were compared to historical specimens using a bivariate scatter plot and a discriminant function (the latter was used to classify recent specimens post hoc). The few recent specimens were not diagnosable as L. l. mearnsi, but instead appear to be intergrades between L. l. mearnsi and L. l. anthonyi Mearns 1898 (the subspecies endemic to Santa Cruz, Santa Catalina, Santa Rosa and Anacapa islands), and are perhaps closer to pure anthonyi. Our data and the species’ natural history and distribution suggest that shrikes currently on San Clemente Island are the result of genetic ‘swamping’ of mearnsi by anthonyi. Under a necessarily typological definition of a subspecies, it is evident that mearnsi is probably no longer diagnosable. However, we conclude that protection of the entire Channel Islands population of the loggerhead shrike would be the best management strategy, as the species has declined drastically throughout the islands.

Abstract: New Pygmy Mammoth (Mammuthus exilis) Localities and Radiocarbon Dates from San Miguel, Santa Rosa, and Santa Cruz Islands, California

Abstract The 1994 discovery and excavation, on Santa Rosa Island, of the most complete pygmy mammoth (Mammuthus exilis) skeleton yet recovered prompted additional research of the California Channel Islands. An intensive, pedestrian survey of mammoth localities tied to GPS coordinates was initiated for the first time in the history of the island mammoth research and has resulted in the discovery and documentation of more than 100 new localities. Several mainland-size mammoth (Mammuthus columbi) elements were recovered. These may represent: 1) ancestral animals; 2) contemporary animals; or 3) late migrant animals. Dental and osteological metric analyses in progress will allow comparisons and contrasts to mainland M. columbi populations. Six new radiocarbon dates from San Miguel and Santa Rosa islands have been added to the eleven published dates for mammoth and mammoth-associated material. These new dates include an AMS bone collagen date of 12,840 ± 410 yr B.P. (CAMS 24429) derived from the right femur of the 1994 skeleton.

Population Structure of the Pacific Angel Shark, Squatina californica (Squatiniformes: Squatinidae), around the California Channel Islands

Starch gel electrophoresis was employed to examine genetic variability in three samples of the Pacific angel shark, Squatina californica, around the California Channel Islands. Gene products of 25 enzyme systems encoded by 29 presumptive loci were examined. Seven loci were polymorphic, with a mean sample heterozygosity of 0.056. F-statistics and contingency chi-square analysis revealed significant genetic divergence between northern samples (Santa Rosa and Santa Cruz Islands) and a southern sample (San Clemente Island). This apparent barrier to gene flow may result from a combination of behavioral characteristics and topography of the sea floor around the California Channel Islands. Significant allele-frequency differences in an elasmobranch species have not been detected previously over such short geographical distances.

Validation of launch vehicle sonic boom predictions

Concern has been raised about the sonic boom levels generated by launch vehicle operations. To address this concern the USAF recently monitored the sonic boom generated by the launch of a Titan IV rocket and the reaction of the local wildlife. The sonic boom generated by this launch intersected the Channel Islands off the coast of Southern California. The sonic booms were recorded by the USAF Boom Event Analyzer Recorder and by DATs with low-frequency microphones on San Miguel, Santa Rosa, and Santa Cruz islands. Before the launch, predictions were made to assess the sonic boom impact on the islands. The prediction model used in this comparison was PCBoom3, a single-event sonic boom model developed by the USAF. This model has been updated to model sonic booms generated by launch vehicles and includes the effect of the rocket plume on the generation of the sonic boom. The measured sonic boom signatures are compared to predictions.

Recruitment of juvenile abalone (Haliotis spp.) measured in artificial habitats.

In September 1989, 45 concrete block habitats were deployed at three sites 25 km apart along the southern shores of Santa Rosa and Santa Cruz Islands, California, at depths of 10-16 m. In October 1989, 7200 small (≈ 41 mm) hatchery-reared red abalone, Haliotis rufescens, were introduced into 36 of the habitats. Nine habitats remained empty as controls. The habitats were surveyed in situ periodically for two years. Sufficient numbers of native abalone, H. rufescens and H. corrugata, were detected (315) to identify spring recruitment events. Habitats with introduced abalone contained more than twice as many native abalone as did empty control habitats during the first year. Average densities of native abalone in the artificial habitats (0.011 m-2) approximated densities of young-of-the-year abalone discovered by previous destructive sampling in natural habitat. Approximately 32% of the introduced abalone survived one year and 24% survived two years. Three to eight artificial habitats were sufficient to detect 20% differences in mean abalone densities during peak spring recruitment events.

Application of the global positioning system to crustal deformation measurements: 3. Result from the southern California borderlands

Five years of measurements from the Global Positioning System (GPS) satellites collected between 1986 and 1991 are used to investigate deformation in the offshore regions of southern California. GPS provides the first practical technique to make precise geodetic measurements in the region. The geodetic network is situated along the California coastline from Vandenberg (120.6°W, 34.6°N) to San Diego, with additional sites on Santa Cruz, San Nicolas, Santa Catalina, Santa Rosa, and San Clemente Islands. The precision of horizontal interstation vectors is subcentimeter, and the interstation vector rate between OVRO and Vandenberg agrees with the very long baseline interferometry derived rate to within one standard deviation. No significant motion is observed in the western Santa Barbara Channel between Vandenberg and Santa Rosa Island, 0.5 ± 1.6 mm/yr, where the quoted uncertainties are one standard deviation. Motions in the eastern Santa Barbara Channel are consistent with compressional deformation of 6 ± 1 mm/yr at N16 ± 3°E. This motion is in agreement with seismicity and an independent geodetic analysis for the period 1971–1987 (Larsen, 1991). San Clemente Island is moving relative to San Diego at the rate of 5.9 ± 1.8 mm/yr at a direction of N38 ± 20°W. The motion between San Nicolas Island and San Clemente Island, 0.8 ± 1.5 mm/yr, is insignificant.

The Miocene Blanca Formation, Santa Cruz and Santa Rose Islands, California--Stratigraphic Correlation and Tectonic History

Geochemical studies of volcanic clasts from the middle Miocene Blanca Formation exposed on Santa Cruz and Santa Rosa Islands confirm earlier studies that suggested correlation of these two occurrences on the basis of stratigraphic position and lithology. Clasts from both areas are calc-alkaline dacite and rhyolite that define smooth trends on element-variation diagrams and possess unusually low incompatible trace-element concentrations and Sr-isotopic ratios when compared to other typical calc-alkaline volcanic suites: Rb ranges from 6 to 60 ppm, Sr from 260 to 575 ppm, and {sup 87}Sr/{sup 86}Sr averages 0.7033. The main exposure of this formation on Santa Cruz Island has been divided into three members. Based on elemental similarities, clasts from the Santa Cruz Near Point exposure are most similar to those from the lower two members, whereas clasts from the Santa Rose exposure are more similar to those from the upper member. Clasts from all three exposures likely were derived from the same volcanic complex before being deposited in a single submarine-fan complex. We conclude that these rocks were erupted and deposited onto the Baja Borderland allochthon by subduction-related volcanism that was active south of the Rivera triple junction. The fan complex was then translated on this allochthonmore » northward relative to the North American craton and rotated {approximately} 90 to 128{degree}CW to its present position.« less

HESPEROPHYCUS SETCHELL & GARDNER, NOM. CONS. PROP., A PROBLEMATIC NAME APPLIED TO A DISTINCTIVE GENUS OF FUCACEAE (PHAEOPHYCEAE)

SummaryHesperophycus harveyanus (Decaisne) Setchell & Gardner (Fucaceae, Phaeophyceae), the type and only known species of its genus, is representative of Fucus L., not of Hesperophycus as described by Setchell and Gardner. Hesperophycus is therefore proposed for conservation with Gardner 1842, on which the generic description was based, as type. The species is redescribed as H. californicus P. C. Silva. It ranges from Santa Cruz, California, to Punta Eugenia, Baja California, but is scarce on the southern California mainland. It occurs on all of the Channel Islands of southern California, but is especially abundant on Santa Catalina and Santa Cruz islands, where it forms an extensive belt in the upper intertidal zone, above Pelvetia.

Earthquake source processes and subduction regime in the Santa Cruz Islands region

Abstract The source process of two large earthquakes that occurred in the Santa Cruz Islands subduction zone has been studied, one with a surface wave magnitude M S = 7.9 in 1966 and the other with M S = 7.7 in 1980. The seismic moment of the 1980 event estimated from long-period surface waves of Global Digital Seismograph Network (GDSN) and International Deployment of Accelerographs (IDA) records is 5.6 × 10 27 dyn cm. Both of these events occurred at a shallow depth (i.e. between 20 and 40 km) with a similar thrust type focal mechanism with a strike (∼ 347°) parallel to the local trench axis, and they are located within 100 km in distance. The 1966 event is a break of a single asperity which ruptured unilaterally to the north along the local trench strike and was truncated sharply at the northern boundary. This rupture pattern and the aftershock area expansion to the north indicate that there was a distinct barrier on the south of the 1966 source area. The major moment release of the 1980 event represents the rupture of this barrier. However, inversion of P-waves with an assumption of a constant focal mechanism failed to constrain the source process thereafter. In particular, the deconvolved source-time functions of the 1980 event do not show such a clear truncation as is observed in the 1966 source process, indicating that some unresolved features followed the peak of the moment release. Nevertheless, the 1-day aftershock area suggests that the rupture propagated to the north into the source area of the 1966 event. We conclude that both earthquakes are subduction events between the Pacific and Indo-Australian plates; the 1966 event is a break of a single asperity and the 1980 event is a break of the remnant asperity which acted as a barrier for the 1966 source rupture. The subduction segmentation inferred from the intermediate-depth seismicity seems to control the mechanical condition of the subduction interface at shallow depths where the two large events took place. This interface created a barrier between the two source areas.

Possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications

SUMMARY Body waveform inversion methods usually assume a constant double-couple source, or a combination of such subevents. Previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption. However, for events where the source area overlaps previously ruptured zones, the conventional inversion methods fail to resolve the source process. For such events the subduction coupling may vary between the mature source area and the previously ruptured zone, causing a variation in the focal mechanism too. We study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 Chilean earthquake (M, = 6.0), the 1978 Kurile (M, = 7.6) and 1980 Santa Cruz Islands (M, = 7.7) earthquakes. For the first event, we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process. The epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events, e.g. the 1963 and 1969 Kurile earthquakes and the 1966 Santa Cruz Is. earthquake, respectively. For each event, one of the focal mechanism solutions shows a substantial strike-slip component. The stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied. Two particular families of stress tensors examined are: (1) the tensors that are optimally orientated with respect to the mature source area and (2) the tensors that have a vertical principal stress direction. The first type of tensors can fully account for the observed slip orientation only for the Chile aftershock, but it comes close to the observed one in the case of the Kurile Island event, and would indeed reactivate the decoupled area at a reasonably low stress level. The second type of tensors can be compatible with the two observed slip orientations in all cases. However, for the Santa Cruz Is. and Kurile Is. earthquakes, the friction law which should be satisfied on each plane requires too high a stress deviation.

Collection of Anastrepha fraterculus on Santa Cruz Island, Galapagos Province, Ecuador

Fruit flies of the genus Anastrepha, family Tephritidae, are major pests in the Western Hemisphere, predominantly in the tropics and subtropics (Stone 1942). Previously, they had been reported from the Galapagos Islands from only a single specimen of Anastrepha fraterculus (Wiedmann) collected in a spider web (Foote 1982). Of six species in six genera of tephritids known from the Islands, A. fraterculus is considered to be the only introduced species, the remaining five being endemic (Foote 1982). The paucity of previously known specimens of this genus from the Islands is undoubtedly a result of inadequate sampling, as the data from the present study suggest. Ample opportunity for colonization by many species of Anastrepha exits, as many known host plants (Norrbom 1985), mostly introduced (Wiggins & Porter 1971, Lawesson 1987), occur on the Islands. Psidium guajava Linnaeus, for example, the common guava or guayaba, which is a known host for 18 species of Anastrepha (Norrbom 1985), has spread over extensive areas of San Cristobal, Isabela, Floreana, and Santa Cruz Islands (Lawesson 1987) following its introduction earlier in the century. In April, 1987, two of us (JE and GC) established McPhail traps (McPhail 1937) on the island of Santa Cruz to sample for the presence of Anastrepha. Eighteen traps were placed in a small (<1 ha) grove of guayaba trees located on a farm approximately 800 meters west of Bella Vista at an elevation of ca. 500 m. Traps were each baited with two yeast hydrolysate tablets dissolved in water and were hung at heights of 1.8-2.5 m above ground in trees which were 3.0-3.5 m tall. They were placed only on branches which bore fruit. All traps were emptied weekly, rebaited, and rehung, with collections made on April 17 and 24 and May 1 and 8. Weather during the sampling period was wet, with rain occurring daily. All insects collected were emptied into a sieve, washed, and placed in jars containing 70% ethanol. In the laboratory, they were transferred to Whirl-Pak bags containing 70% ethanol, labeled, and sent to the United States for sorting and identification. All Anastrepha specimens were removed, placed in separate alcohol vials, and identified to species. Each of the 18 traps caught Anastrepha, but no trap caught them on every sampling date. A total of 245 specimens was collected during the 72 trap weeks included in the study (one trap week = one trap operated for one week). Catches ranged from 0 to 34 Anastrepha per trap in a given week and to 38 per trap over the entire four weeks. Mean catches/trap/week were 3.4 +-5.3, while mean catches per trap over the four-week period were 13.6 ?+10.8. Total combined trap catches/week were 11, 72, 115, and 47 for trap weeks 1-4, respectively.

A SURVEY OF WILD SWINE IN THE UNITED STATES FOR EVIDENCE OF HOG CHOLERA

The results of surveillance for hog cholera (HC) in wild swine (Sus scrofa) collected from throughout the United States from 1979 to 1987 are presented. Sera collected from 1,218 wild swine and tissues from 637 were evaluated for HC antibodies and virus, respectively. Included within this surveillance were samples from Santa Cruz and Santa Rosa Islands, California, where HC virus had been deliberately introduced into wild swine during the 1950's in attempts to eradicate these animals. All evaluations were considered negative for HC. It appears that the HC virus does not maintain itself in dispersed swine populations and that wild swine have not remained a reservoir of HC since its eradication in domestic swine in the United States.

The genus Myndus (Hemiptera: Cixiidae) in the solomon islands and Vanuatu and its relation to foliar decay of coconut palms in Vanuatu

AbstractThe species of the cixiid genus Myndus occurring in the Solomon Islands and Vanuatu are reviewed. M. macfarlanei sp. n. is described from Santa Cruz Islands. It is distinguished from M. mavors Fennah and M. taffini Bonfils, both of which are redescribed and illustrated. All species have been collected from coconut palms, and M. macfarlanei also from areca palm (Areca catechu). M. taffini has been previously confirmed as the vector of foliar decay of coconut palms in Vanuatu.

Some conservation problems encountered with turmeric on ethnographic objects

The pH dependency of turmeric, used as a dye or pigment on ethnographic objects from the Santa Cruz Islands, can present a conservation problem. Great care must be taken with the cleaning, consolidation, repair, storage and display of objects of this nature. A section on the analysis of suspected turmeric is included.

Two New Species of Scincid Lizards of the Genus Emoia from Santa Cruz and Duff Islands, Solomon Islands

DAWSON, C. E. 1977. Synopsis of syngnathine pipefishes usually referred to the genus Ichthyocampus Kaup, with description of new genera and species. Bull. Mar. Sci. 27:595-650. . 1980. Notes on some Siboga Expedition pipefishes previously referred to the genus Syngnathus. Bijdr. Dierk., Amsterdam 50:221-226. . 1982a. The pipefishes (subfamilies Doryrhamphinae and Syngnathinae). Fishes of the Western North Atlantic, Sears Foundation for Marine Research Mem. 1:4-172.

Miocene Blanca Fan, Northern Channel Islands, California: Small fans reflecting tectonism and volcanism

Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively.

Effects of lateral heterogeneity and source process time on the linear moment tensor inversion of long-period Rayleigh waves

abstractSpectra of mantle Rayleigh waves recorded on the IDA network are inverted to determine the seismic moment tensor of the 9 June 1980 California-Mexico Border earthquake, the 29 July 1980 Vanuatu Islands earthquake, and the 9 July 1980 Santa Cruz Islands earthquake. Examinations are made to correct for phase velocity lateral heterogeneity and source process time. A simple regionalization (stable continent, tectonic region, young ocean, and old ocean) improves results of the linear inversion, but the phase correction is not large enough, and the discontinuous change of phase velocity across the boundary between regions causes an artificial rapid change in apparent phase velocity as a function of azimuth. Therefore, a more detailed but gradual representation of the lateral heterogeneity is desirable to correct for the propagation effect in the linear inversion. A source process time which consists of the nondirectional part of the apparent duration of main faulting and the delay time of the faulting from initial break is estimated by a phase analysis of Rayleigh waves. The source process time is generally proportional to the seismic moment on the log-log scale, but some earthquakes deviate considerably from the general relation. Therefore, the measurement of the source process time should be made before the moment tensor inversion. The phase errors introduced by the lateral heterogeneity and source process time may cause a bias to low scalar moment.

Red cell enzyme and serum protein types in a population from Ndeni (Santa Cruz Islands).

Data for 14 red cell enzyme systems, haemoglobin and four serum proteins are presented for 351 people from the island of Ndeni in the Santa Cruz group of the British Solomon Islands Protectorate. The results support the view based on linguistic studies that the Ndeni population is derived from a mixing of older Papuan and later Austronesian-speaking peoples.

Aedes albopictus in the Solomon and Santa Cruz Islands, South Pacific

Surveys of mosquitoes in the South Pacific up until 1977 have shown the presence of Aedes albopictus only as far east as Papua New Guinea. During the visit to the Solomon Islands in 1978 to collect members of the Aedes (Stegomyia) scutellaris complex, Ae. albopictus was found in large numbers on Guadalcanal and was also present in the Santa Cruz Islands. This species has been incriminated as a vector of dengue haemorrhagic fever.

Tectonic rotations of the Santa Monica Mountains region, western Transverse Ranges, California, suggested by paleomagnetic vectors

The paleomagnetism of middle to late middle Miocene volcanic rocks from regions of the western Transverse Ranges suggests that large amounts of subsequent clockwise tectonic rotation has occurred. We studied rocks from five sites in the western Santa Monica Mountains, Conejo Hills, and Anacapa Island. East declinations of from 64° to 81° were found, compared to expected Miocene declinations of 0°, and inclinations were too shallow by up to 21° for the present latitude. Preliminary data from Santa Cruz and San Miguel Islands suggest similar but larger rotations. Stratigraphically higher units show the least amount of rotation, which may indicate that about 60° of rotation occurred primarily during middle and late Miocene time. North-pointing directions can be restored by rotating the northern Channel Islands and Santa Monica Mountains counterclockwise about a pivot near the eastern end of the range. This restoration also changes paleocurrent directions in Eocene and Oligocene rocks from north to west, which is consistent with data from surrounding regions. Shallow remanent inclinations suggest northward movement of this block of ∼10° since early Miocene time.